The imbalance of the CNP ratio of influent water will lead to many problems in the sewage system, such as sludge expansion, effluent exceeding the standard and other problems, and it cannot be compensated by changing the operating conditions, and the CNP ratio needs to be adjusted to the corresponding ratio to solve the problem.

1. Methods for determining CNP ratio imbalance

How to judge the CNP ratio imbalance, among which you must first determine what process your process is? Carbon removal? Denitrification? Phosphorus removal? Nitrogen and phosphorus removal? The ratio of CNP ratio for different processes is different!

How to judge? Very simple! Remember these judgment points: the carbon removal process is simple aeration, mainly to remove COD, such as simple aeration tank, contact oxidation, classic SBR, etc.; Denitrification is the alternation of hypoxia and aerobic that is experienced, mainly to remove TN, such as the AO process for in-band reflow; The phosphorus removal process is to go through the alternation of anaerobic and aerobic, mainly to remove TP, such as the AO process without internal reflux; The denitrification and phosphorus removal process is a process that combines biological nitrogen removal and biological phosphorus removal process, which mainly removes TN and TP simultaneously, such as AAO process, oxidation ditch process, etc.

After distinguishing what process you are, you can determine the range of carbon, nitrogen and phosphorus ratio:

Carbon removal process: CNP ratio 100:5:1

Denitrification process: CN ratio 4-6, take the median value 5, this process can ignore the removal of TP

Phosphorus removal process: CP ratio 15, this process can ignore the removal of TN

Nitrogen and phosphorus removal process: It is necessary to meet both CN ratio 4-6 and CP ratio 15

According to the CNP ratio of the influent water plus the process type, you can judge whether the CNP ratio is unbalanced, in this range the CNP ratio can be considered to be unbalanced, and if it is not in this range, CNP can be considered to be unbalanced!

2. Adjustment of CNP ratio imbalance

Therefore, the premise of the successful adjustment of CNP ratio imbalance is the correct amount of nutrients, and the following also provides you with a different nutritional dosage calculation idea!

The premise of the calculation of the dosage is the unit conversion, the author has always emphasized this, many friends miscalculate mainly or the unit is not converted or converted incorrectly! Write down the conversion process and remember this ratio so you can't make mistakes:

1PPM=1mg/L=1g/m^3=0.001kg/m^3

According to the above conversion relationship, the following calculation of the dosage must be converted into a unified unit before it can be substituted into the calculation!

1. Carbon source addition

1) Carbon removal process:

X = inlet * (20 * N difference 1-C difference) / carbon source COD equivalent where: X - carbon source input N difference 1 - influent ammonia nitrogen (or TKN) - ammonia nitrogen C difference required by discharge - influent COD - effluent COD

2) Denitrification process:

Y = inlet * (5 * N difference 2-C difference) / carbon source COD equivalent where: Y - carbon source dosage N difference 2 - influent TN - TNC difference of discharge requirements - influent COD - effluent COD

3) Phosphorus removal process:

Z = inlet * (15 * TP difference - C difference) / carbon source COD equivalent where: Z - TP difference in carbon source dosage in phosphorus removal process - TPC difference in influent TP - TPC difference in discharge requirements - influent COD - COD denitrification and phosphorus removal process in effluent:

W = water intake * (5 * N difference 2 + 15 * TP difference - C difference) / carbon source COD equivalent where:

W - N difference of carbon source dosage in nitrogen removal and phosphorus removal process 2 - TN in influent water - TNTP difference in discharge requirements - TPC difference in influent TP - influent COD - COD in effluent water

2. Nitrogen source addition

The addition of nitrogen sources is in the carbon removal process, the carbon source is sufficient, the nitrogen source is lacking, in this case, the CN ratio we use is 100:5 of the carbon removal process, that is, 20:1! Formula:

N=water inlet * (C difference 1/20-N difference 1) / TKN content in nitrogen source

Thereinto:

N - nitrogen source dosage

C difference 1 - influent COD - CODN for discharge requirements Difference 1 - influent ammonia nitrogen (or TKN) - ammonia nitrogen for discharge requirements

3. Addition of phosphorus salt

The addition of phosphorus salt is the same as the addition of nitrogen source, both in the carbon removal process, the carbon source is sufficient, the phosphorus source is lacking, in this case, the CP ratio we use is 100:1 of the carbon removal process! Formula:

P = water intake * (C difference 1/100-TP difference) / phosphorus content in phosphorus salt

Thereinto:

P - phosphorus salt dosage

C Difference 1 - CODTP difference in influent water - CODTP difference in discharge requirements - TP in influent water - TP for discharge requirements